First-Principles study of tris(8-hydroxyquinoline)iron(III) molecules: A promising spin filter material

Using first-principles calculations, we have systematically investigated the structural, electronic, and magnetic properties of facial and meridional tris (8-hydroxyquinoline)iron(III) (Feq$_{3})$ molecules, solvent-free Feq$_{3}$ crystals and thin films. Our calculation results show that both Feq$_{3}$ isomers have a high spin state of 5 $\mu_{B}$ as the ground state when an on-site Hubbard-U term is included to treat the highly localized Fe 3$d$ electrons, in agreement with experiment, while the standard DFT calculations produce a low spin Fe state of 1 $\mu_{B}$. Furthermore, the freestanding Feq$_{3}$ films are found to be paramagnetic, but become Ferromagnetic (FM) within each layer when deposited on a NiFe substrate. This is induced by a strong anti-ferromagnetic (AFM) coupling between the first molecular layer and FM substrate. Also, an AFM coupling is found between the molecular layers. These findings suggest that Feq$_{3}$ molecular films may serve as a promising spin filter material in spintronic devices.